An absorbent article such as a diaper, a sanitary napkin or an incontinence guard will normally include a liquid-permeable outer sheet, a liquid-impervious barrier sheet and an absorbent body located therebetween. An absorbent article of one of the aforesaid kinds has a generally rectangular shape, including two long sides and two short sides.
The outer sheet is that part of the absorbent body which lies proximal to the wearer's body in use, while the barrier layer is that part of the absorbent article which lies distal from the wearer's body. The outer sheet is normally comprised of perforated plastic film, nonwoven or a plastic and nonwoven laminate. The plastic may be a thermoplastic material, such as polyethylene. The nonwoven material may be comprised of natural fibres, such as cellulose or cotton fibres, or synthetic fibres, such as polyethylene, polypropylene, polyurethane, nylon or regenerated cellulose fibres.
The purpose of the outer sheet of an absorbent article of the aforesaid kind is to conduct fluid into the article, and to prevent rewetting of the wearer's skin and therewith create a dry surface in contact with the skin. A dry surface on that part of the article which lies against the wearer's skin in use is important to the comfort of the wearer and also in avoiding skin irritation.
The barrier layer is produced in a liquid-impermeable material and functions to prevent liquid leaking from the underside of the absorbent article. The barrier layer may be comprised of any type of material that will fulfil the criterion of liquid impermeability and which is sufficiently flexible for the purpose intended. Examples of suitable barrier layer materials are plastic films, nonwoven and laminates thereof. The plastic film may be comprised, for instance, of polyethylene, polypropylene or polyester.
The absorbent body is normally produced from cellulose pulp. The pulp may exist in rolls, bales or sheets that have been dry-defibrated and transformed in a fluffed state to a pulp mat. As before mentioned, the absorbent body may be comprised of cellulose fibres. Examples of other fibres conceivable in this regard are cotton fibres and synthetic fibres. It is also known to use in the absorbent body a foamed material.
So-called superabsorbents are sometimes used with the intention of enhancing the liquid-retaining capacity of the absorbent body, superabsorbents being polymers that are capable of absorbing several times their own weight of water or body fluid. Examples of such superabsorbents are polyacrylates, starch or modified cellulose, such as carboxy-methyl cellulose.
The superabsorbent is normally added to the absorbent material in powder form, and is either admixed uniformly or is concentrated to certain parts of the absorbent body. The superabsorbent can also be supplied to the absorbent body in the form of a band or a film. The advantage with this method of administration is that the superabsorbent can be easily applied in the intended manner and in the correct amount. Application of the superabsorbent in the form of a film or band also avoids the potentially harmful dust that is generated when handling all types of powder material.
The drawback with superabsorbent in film or band form, is that this method of administration can easily result in so-called gel-blocking. Gel-blocking occurs because of the rapid swelling of the superabsorbent when liquid is applied, therewith preventing further spreading of liquid down through the absorbent body. Naturally, this can also occur when the superabsorbent is applied in powder form, although the risk of gel-blocking is naturally greater when the superabsorbent has been concentrated to a smaller area of the absorbent body, as is the case when applying superabsorbent in a film or band form.